WO2008050379A1

WO2008050379A1 - Gear and gear drive unit

Info

Publication number: WO2008050379A1
Application number: PCT/JP2006/321012
Authority: WO
Inventors: Masanori Satou; Yoshiyasu Nakano; Katsufumi Abe
Original assignee: Ntn Corporation
Priority date: 2006-10-23
Filing date: 2006-10-23
Publication date: 2008-05-02
Also published as: JPWO2008050379A1

Abstract

A gear, and gear drive unit, wherein the formation of oil film between tooth surfaces of gears rotating at high speed is satisfactory to thereby prevent the occurrence of pitching, abrasion and scoring and also prevent any temperature rise and wear so that the durability thereof can be enhanced. There is provided a gear having a tooth surface furnished with an indefinitely large number of dimples of minute concave configuration at random, wherein the area ratio of dimples in the dimpled surface is in the range of 35 to 75%. Accordingly, the tooth surface gains a high oil-film forming capability, so that a prolonged life duration can be ensured even under conditions such that the thickness of the oil film is extremely small in low viscosity/thin lubrication.

Description

Specification

Gear and gear drive device

Technical field

The present invention relates to a gear and a gear driving device, and can be applied to, for example, a gear and a gear driving device used in a power transmission unit or a gear pump of an automobile transmission.

Background art

[0002] For example, Patent Document 1 discloses a gear in which countless dents are randomly provided on the tooth surface. The average area of these micro-indentations is 35 to 150 111 ² , the ratio of the micro-indentations to the surface is 10 to 40%, and the average surface roughness with micro-indentations is RmaxO. 6 to 2.5 μm. m, the parameter Sk of the surface roughness of the tooth surface with a small dent is set so that Sk≤—1.6. This improves the ability to form an oil film on the surface and sufficiently forms an oil film between the tooth surfaces of the gear, thereby preventing damage caused by poor lubrication such as peeling from the surface of the gear and improving durability. ing.

Patent Document 1: Japanese Utility Model Publication No. 4 56254

Disclosure of the invention

Problems to be solved by the invention

[0003] In recent years, parts where gears are used, such as automobile transmissions, are becoming smaller and have higher output power, and the usage environment such as lowering the viscosity of lubricating oil tends to be high load and high temperature. For this reason, gears are changing to a more severe lubrication environment than ever, and wear due to poor lubrication, surface-origin-type delamination, reduced fatigue life due to high surface pressure, and delamination in a foreign environment are increasingly occurring. It's getting easier. In other words, the multistage transmission tends to increase the torque and load acting on the gears used there, as well as the number of rotations, and the gears are required to have downsizing and high-speed rotation functions. . As a result, the lubrication conditions for gears have become increasingly severe, and wear and damage due to poor lubrication are likely to occur. For this reason, even if various conditions of the tooth surface of the gear are set as described in Patent Document 1, the effect may not be sufficiently exhibited. [0004] An object of the present invention is to sufficiently form an oil film between the tooth surfaces of a gear rotating at high speed, to prevent occurrence of pitching, abrasion and scoring, and to improve durability by preventing temperature rise and wear. It is an object of the present invention to provide a gear and a gear driving device using such a gear.

Means for solving the problem

[0005] In order to solve the above-described problems, the gear of the present invention has an infinite number of minute concave recesses on the tooth surface, and the area ratio of the recesses on the surface provided with the recesses is 35 to 75%. It is in the range of.

[0006] As described above, in the gear and the gear driving device of the present invention, the oil film forming ability is improved by setting the area ratio of the indentation in the surface provided with the indentation in the tooth surface within the range of 35 to 75%. Therefore, long life can be obtained even under the condition of extremely thin oil film thickness under dilute lubrication.

[0007] Further, in this gear, when the surface roughness parameter Ryma X in the axial direction of the surface provided with the depression is set within the range of 1.3 ^ πι≤Κγπι _& χ≤3.0 m, further oil film formation Ability can be improved. Where the parameter Rymax is the maximum value of the maximum height per reference length (ISO 4287: 1997) o

[0008] Further, in this gear, when the surface roughness in the axial direction of the surface provided with the indentation is represented by the parameter Rq ni, Rqni is within the range of 0.13 μm ≤ Rqni ≤ 0.5 μm. By setting it, the oil film forming ability of the tooth surface can be further improved. The parameter Rqni is the square root of the roughness center line force, the square root of the height deviation up to the roughness curve, integrated over the measured length interval, and averaged over that interval, also known as the root mean square roughness. Say. Rqni is obtained by numerical calculation of the cross-sectional curve and roughness curve force recorded on an enlarged scale, and is measured by moving the stylus of the roughness meter in the width and circumferential directions.

[0009] Further, a nitrogen-enriched layer can be formed on the surface of the gear. The nitrogen-enriched layer is a layer having an increased nitrogen content formed on the tooth surface, and can be formed by a process such as carbonitriding, nitriding, or nitriding. The fatigue life can be greatly improved by forming the nitrogen-enriched layer and making the austenite grain size finer as the grain size number of the austenite grains in the nitrogen-enriched layer exceeds 10. Austenai When the grain size number is 10 or less, the fatigue life is not greatly improved. Therefore, the range is over 10 and usually 11 or more. The finer the austenite grain size, the better, but usually it is difficult to obtain a grain size number exceeding 13. Note that austenite grains appear when heated to a temperature above the transformation point during heat treatment, and when transformed, they transform to a different structure, but after transformation, traces of austenite grain boundaries remain, and the traces remain. It refers to a crystal grain based on

[0010] The nitrogen content in the nitrogen-enriched layer is preferably in the range of 0.1% to 0.7%. On the other hand, if the nitrogen content is less than 0.1%, the effect cannot be obtained, and the fatigue life is reduced particularly under the condition of contamination. If the nitrogen content is more than 0.7%, voids called voids will be formed, or the retained austenite will increase so much that the hardness will not be achieved, resulting in a short life. For the nitrogen-enriched layer formed on the tooth surface, the nitrogen content is the value at the surface layer of 50 m of the tooth surface, and can be measured by, for example, EPMA (wavelength dispersive X-ray microanalyzer).

The invention's effect

[0011] As described above, according to the present invention, by providing an infinite number of minute concave recesses, the tooth surface becomes a minute rough surface and an oil film can be easily formed. Since the indentation becomes an oil reservoir, the oil film on the sliding surface can be formed reliably. As a result, the temperature rise can be reduced and the metal contact between the tooth surfaces of the meshing gears can be relaxed. Pitting, abrasion, and scoring can be achieved even in the high-speed rotation region. Can be prevented. Therefore, even if the oil film thickness is extremely thin under low viscosity and dilute lubrication, a long life of the gear and the gear driving device can be obtained. Furthermore, by improving the fatigue life of the surface layer of the toothed wheel, it is possible to obtain excellent cracking resistance and aging resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] Fig. 1 shows an example of a transmission used in an automobile. An input shaft 2, a drive pion 3, and an output shaft 4 are arranged in series in a case 1, and a counter parallel to the output shaft 4 is provided. Shaft 5 and reverse shaft 6 are arranged A gear 7 group is attached to the drive pion 3 and each shaft 2, 4 and 5, and the input shaft 2 can be fitted by changing the meshing of each gear 7 group by the operation from the outside of the case 1. Change to the output shaft 4 or reverse and take it out! In this transmission, as the input shaft 2 rotates, the oil accumulated in the oil pan (not shown) is splashed onto the gear 7, lubricates the gear 7 group, the bearings 8, 9, etc., and returns to the oil pan. In other words, the transmission includes a gear driving device having a driving gear driven by a driving force and a driven gear driven by meshing with the driving gear.

FIG. 2 shows a gear 7 constituting a part of the gear driving device. The tooth surface 7a of this gear is a minute rough surface in which countless independent minute depressions are randomly formed. This fine rough surface has an indentation area ratio of 35 to 75%. Also, the surface roughness parameter Rymax in the axial direction of the surface provided with the indentation is within the range of 1.3 ^ m≤Rymax≤3.O / zm. Further, the surface roughness parameter Rqni in the axial direction of this surface is It is within the range of 0.13 ^ m≤Rqni≤0.5 m. As a surface cleaning treatment for obtaining such a fine rough surface, a desired finished surface can be obtained by special barrel polishing, but is not limited thereto, and for example, a shot or the like may be used. .

[0015] The surface layer of the tooth surface 7a of the gear wheel 7 is formed with a nitrogen-enriched layer by a treatment such as carbonitriding, nitriding, or nitriding, and the grain size number of the austenite crystal grains in the nitrogen-enriched layer is 10 It is set to a range exceeding the number, for example, number 12. The nitrogen content in the surface layer 50 m of the tooth surface 4a is set in the range of 0.1 to 0.7%.

FIG. 3 is a view showing the microstructure of the tooth surface of the gear, particularly austenite grains. Fig. 3 (A) shows a gear having an austenite grain size of JIS standard grain number 12 (invention example), and Fig. 3 (B) shows a gear having a grain size number 10 (comparative example). FIGS. 4 (A) and 4 (B) show the austenite grain sizes illustrated in FIGS. 3 (A) and 3 (B). The average particle size in Fig. 3 (A) was 5.6 m as a result of measurement by the intercept method.

[0017] Thus, the gear of the gear drive device of the present invention is provided with an infinite number of minute concave recesses, so that the tooth surface becomes a minute rough surface and an oil film is easily formed. In addition, since this dent becomes an oil reservoir, an oil film can be reliably formed on the sliding surface. Because of this, itching The metal contact between the tooth surfaces 7a of the mating gear 7 can be alleviated, and the temperature rise can be reduced, and the occurrence of pitching, abrasion and scoring can be prevented even in the high-speed rotation region, and the life can be extended. Can do. In particular, by setting the area ratio of the depressions on the surface with the depressions within the range of 35 to 75%, it becomes possible to prevent oil film breakage even under lean lubrication, and even under extremely thin oil film conditions. Long life can be obtained.

[0018] Further, by setting the surface roughness parameter Rymax in the axial direction of the surface provided with the indentation within the range of 1.3 μm ≤ Rymax ≤ 3. O / zm, or in the axial direction of this surface By setting the surface roughness parameter Rqni within the range of 0.13 / ζ πι≤Ι¾ηί≤0.5 m, the oil film forming ability can be further improved.

[0019] This gear has a nitrogen-enriched layer on the surface layer, and the austenite grain size number in this nitrogen-enriched layer exceeds 10, so the austenite grain size becomes finer and the fatigue life is greatly improved. can do.

[0020] If the nitrogen content in the nitrogen-enriched layer is less than 0.1%, the fatigue life under the contamination condition decreases, and conversely if more than 0.7%, voids called voids are formed. In addition, the amount of retained austenite increases too much and the hardness is not obtained, resulting in a short life. For this reason, it is possible to extend the life of the gear by setting the nitrogen content within the range of 0.1% to 0.7%.

[0021] Therefore, the gear of the present invention can obtain a long life even under the condition that the oil film thickness is extremely thin under low viscosity and lean lubrication, and the gear drive of the present invention using such a gear is used. The device can have a long life. Furthermore, by improving the fatigue life of the surface layer, it is possible to obtain excellent crack strength and aging resistance.

As described above, the gear of the present invention is excellent in pitching resistance, abrasion resistance, and scoring resistance, and is therefore optimal as a gear 7 for an automobile transmission as shown in FIG. In addition, two to three sets of planetary gear mechanisms are normally used for automatic transmissions (AT) for automobiles, and the reduction ratio varies by fastening the sun gear, carrier, and ring gear of these planetary gear mechanisms with a clutch. It has become. Therefore, it is preferable to apply the surface texture of the present invention to the sun gear, planetary pinion, ring gear and the like in such a planetary gear mechanism. [0023] By the way, in a pair of gears that mesh with each other, even if a surface treatment that satisfies the surface properties according to the present invention is performed only on the tooth surfaces of one gear, both effects such as long life can be obtained. It is more effective to apply a surface treatment that satisfies the surface properties according to the present invention to the tooth surface of the gear.

[0024] It should be noted that the gear of the present invention can of course be used for various gear drive devices other than the automobile transmission.

Example 1

[0025] In order to show the usefulness of the present invention, first, the life of the gear was evaluated. The tooth surface of the gear makes rolling contact and sliding contact with the tooth surface of the other side, and the contact is in a form according to the contact state between the race of the rolling bearing and the raceway. Therefore, it is considered that the life evaluation of gears can be evaluated by the life test evaluation of rolling bearings. From this viewpoint, the present inventors conducted a life test of the rolling bearing under the conditions described below. When measuring the surface properties represented by these parameters for components such as rolling elements and rolling rings of rolling bearings, even one measured value can be relied on as a representative value. It is good to decide. The measurement methods and conditions of the parameters Ryni, Rymax, Sk, and Rqni measured in this example are as follows. The parameter Ryni is the average value of the maximum height for each reference length, that is, the reference length is extracted from the roughness curve in the direction of the average line, and the distance between the peak line and the valley bottom line of this extracted part. Is a value measured in the direction of the vertical magnification of the roughness curve (ISO 428 7: 1997). The norm Sk indicates the degree of distortion (skewness) of the roughness curve (ISO 428 7: 1997), and is a standard statistic to know the asymmetry of the uneven distribution. In a symmetric distribution such as a Gaussian distribution, the Sk value is close to 0. When the convex and concave portions are deleted, the Sk value is negative, and in the opposite case, the Sk value is positive.

[0026] Parameter calculation standard: JIS B 0601: 1994 (Surfcom JIS 1994)

Cut-off species additional U: Gaussian

Measurement length: 5 λ

Cut-off wavelength: 0.25mm

Measurement magnification: X 10000

Measurement speed: 0.30mm / s Measurement location: Roller center

Number of measurements: 2

Measuring device: Surface roughness measuring instrument Surfcom 1400A (Tokyo Seimitsu Co., Ltd.)

[0027] In addition, in order to quantitatively measure the indentation, the roller surface is enlarged, and the image power can be quantitatively measured by a commercially available image analysis system. Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 2001-183124, if a surface texture inspection method and a surface texture inspection apparatus are used, stable and accurate measurement can be performed. In this method, light is irradiated onto an inspection surface having a curvature, the inspection surface is photographed with a camera, the brightness of the image of the inspection surface photographed with this camera is measured, and the bright portion of the measured brightness is measured. A surface texture inspection method that inspects the surface texture of the surface to be inspected using a light-dark pattern formed with the contrast of the dark area. The brightness distribution of the image to be measured is obtained by irradiating light in the direction of the optical axis of the camera. By positioning the inspection surface so that the position showing the peak value coincides with the optical axis of the camera, shading (luminance distribution) due to the curvature of the inspection surface is suppressed. In addition, light is irradiated in the direction of the optical axis of the camera, and the brightness distribution of the measured image is the origin of the portion of the inspection surface corresponding to the position where this brightness distribution shows the peak value, and the symmetry axis of curvature. Approximate the one-dimensional luminance distribution along each orthogonal coordinate axis with an approximate function, and remove the luminance distribution of the image using these approximate functions. Using the peak value of the luminance distribution as a reference value, the luminance of the measured image corresponding to each coordinate position is corrected, and the surface properties of the inspection surface are inspected with this corrected luminance pattern, thereby reducing shading. Surface texture can be inspected with no light / dark pattern. In addition, when measuring the area ratio and average area of the indentation for components such as rolling elements and rolling rings of rolling bearings, as with the above parameters, a single measured value can be relied on as a representative value. It is good to measure two places that face each other in the diameter direction. The measurement conditions are as follows, for example.

[0028] Area ratio: smaller than the binary threshold value ((bright area brightness + dark area brightness) / 2)!

Average area: Total black area Z total

Viewing field: 826 m X 620 m Measurement location: Roller center

Number of measurements: 2

[0029] Fig. 5 shows an example of a test rolling bearing. This rolling bearing 10 is a needle roller bearing in which a needle roller 12 is incorporated in an outer ring 13 as a rolling element. It has come to support. The following describes the results of a life test conducted on a variety of needle roller bearings with different surface finishes on the needle roller surface. As shown in Fig. 6, the needle roller bearing used in the life test has 15 outer diameters Dr = 33 mm, inner diameter dr = 25 mm, needle roller 12 diameter D = 4 mm, and length L = 25.8 mm. This is a bearing with a cage 15 using needle rollers. Five types of needle bearings with different surface roughness finishes were produced as test bearings. In other words, bearing A (comparative example) with super-finish after grinding, bearing B (comparative example) with numerous indentations of small concave shapes randomly formed, bearing C (example), bearing D (example) And bearing E (Example).

[0030] The test apparatus used is a radial load tester 16 as schematically shown in FIG. 7, in which test bearings 10 are mounted on both sides of the rotating shaft 17, and a test is performed by applying rotation and load. The finish of the inner race (partner shaft) used in the test is RaO. 10 to 0.16 / z m of polished finish. The water race (outer ring) is also common. The test conditions are as follows.

[0031] Bearing radial load: 19613N (2000kgf)

: 4000mm " ¹

Lubricant: Crisecoil H8 (2cst under test conditions)

[0032] Fig. 8 shows a list of characteristic values of the surface finish of each test bearing and the oil film parameter Λ.

The life test result under = 0.13 is shown. As shown in the figure, the life ratio of each test bearing to the bearing A with no depression is 1.6 times for bearing B, 2.0 times for bearing C, 3.8 times for bearing D, and 4 for bearing E. It was 0 times. As is apparent from this data, the bearing rollers D and E whose surface has been treated so that the surface of the needle roller satisfies the surface shape according to the present invention have a low viscosity and a dilute extremely low oil film parameter Λ = 0.13. Even under extremely severe lubrication conditions, it is possible to obtain a long-life effect that is at least twice that of bearing A, which has no dents. Therefore, the gear according to the present invention in which the tooth surface is set in the above numerical range can obtain a long and long life effect.

Example 2 Next, a gear pitching test was performed using a spur gear fatigue tester shown in FIG. 9, and the pitching strength was evaluated. In FIG. 9, the drive-side gear 31 (29 teeth) and the driven-side gear 32 (30 teeth) are attached to one side of each rotary shaft 33, 34, and the drive-side shaft 33 is not shown in the figure. It is driven by. In addition, torque is loaded by a load lever 35 and a weight 36 attached to the shaft 33 on the drive side. Two types of drive side gears 31 were prepared depending on whether or not the surface treatment according to the present invention was performed. The details of the test conditions are as follows.

[0034] Testing machine: Spur gear fatigue testing machine

Drive-side gear: Outer diameter 79 mm, Inner diameter 35 mm, Tooth width 8.2 mm, SCr420 (Carburizing), 29 teeth

Driven gear: outer diameter φ 79mm, inner diameter φ 35mm, tooth width 15mm, SCr420 (carburizing treatment

), 30 teeth

Rotation speed: 3500min ^_1

Tonolek: 186N'm (19kgf'm)

Lubricating oil temperature: 80 ° C

Lubricating oil: ATF oil

[0035] The data of the gear pitching test are shown in Figs. 10 (a) to 10 (c). Fig. 10 (a) shows the result (comparative example) when surface treatment is applied to both the drive side and driven side gears, and Fig. 10 (b) shows the drive side gear. FIG. 10 (c) shows the results (Example) when the tooth surface is treated so that the surface properties according to the present invention are satisfied. FIG. 10 (c) shows the teeth of the drive side gear and the driven side gear. The results (Examples) in the case of using the surface treated so as to satisfy the surface properties according to the present invention are shown on the surface. From these, it can be confirmed that the pitching life is improved more than 2 times in the case of Fig. 10 (b) and more than 3 times in the case of Fig. 10 (c) compared to the case of Fig. 10 (a). .

Example 3

[0036] Next, manufactured products 1 to 5 and comparative products 1 to 3 were manufactured, and these were tested for the relationship between the nitrogen content and the life of the test piece under the condition of contamination, and the results are shown in FIG. Shown in In this test, needle roller bearings shown in Fig. 5 and Fig. 6 were used for the implemented product and comparative product, and the surface of the roller was used. An infinite number of minute concave recesses as shown in the embodiment of FIG. 8 are formed. The crystal grain size is measured based on the JIS G 0551 steel austenite grain size test method. The test conditions are as follows.

[0037] Radial load: 17. 64kN

Axanole load: 1. 47kN

Rotation speed: 2000min ^_1

Hard foreign matter contamination: lgZL

[0038] From Fig. 11, it can be seen that, for the products 1 to 5, the nitrogen content and the foreign material life are in a substantially proportional relationship. However, the comparative product 3 with a nitrogen content of 0.72 should have an upper limit of 0.7 for the nitrogen content in light of the extremely reduced lifespan of contamination. In addition, it can be seen from Example 1 and Comparative Product 1 that the lower limit of the nitrogen content should be 0.1. Further, in light of the fact that the life of the comparative product 2 having a nitrogen content within the above range is reduced, the austenite grain size is preferably a value exceeding 10.

[0039] The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Brief Description of Drawings

[0040] [FIG. 1] Partial cross-sectional view of an automobile transmission

[Fig.2] Enlarged perspective view of the essential parts of the gear

FIG. 3 is a diagram showing the microstructure of gears, particularly austenite grains, where (A) is a gear according to an example of the present invention, and (B) is a conventional gear.

[FIG. 4] (A) shows the austenite grain boundary illustrated in FIG. 3 (A), and (B) shows the austenite grain boundary illustrated in FIG. 3 (B).

[Fig.5] Cross section of needle roller bearing

[Fig. 6] Cross section of needle roller bearing used for life test

[Fig.7] Partial sectional view of the test equipment

[Figure 8] Test results of Example 1 [Fig.9] Partial perspective view of spur gear testing machine

[Fig. 10] (a) Test result of Comparative Example in Example 2 and (b), (c) Test result of Example [Fig. 11] Test result of Example 3

Explanation of symbols

2 Input shaft

4 Output shaft

5 Counter shaft

7 ¾ "car

10 Rolling bearing

Claims

The scope of the claims

[1] An infinite number of minute concave depressions are provided on the tooth surface,

A gear having an indentation area ratio within a range of 35 to 75% on the surface provided with the indentation.

[2] Surface roughness parameter Rymax in the axial direction of the surface provided with the indentation is 1.3 / z m ^ Rymax ^

3. The gear according to claim 1, which is in a range of 0 m.

[3] The surface roughness parameter Rq in the axial direction of the surface provided with the depression is 0.13 / ζ πι≤Ι¾ηί≤0.

The gear according to claim 1 or 2, wherein the gear is within a range of 5 µm.

[4] The gear has a nitrogen-enriched layer on a surface layer, and the austenite crystal grain size number in the nitrogen-enriched layer is in a range exceeding # 10. The gear according to any one of the above.

[5] The gear according to claim 4, wherein the nitrogen content in the nitrogen-enriched layer is in the range of 0.1% to 0.7%.

[6] The nitrogen content is a value at a surface layer of a tooth surface of 50 μm.

A five-car troubled car.

[7] In a gear driving device having a driving gear driven by a driving force and a driven gear driven by engagement with the driving gear,

7. A gear driving device, wherein at least one of the driving gear and the driven gear is the gear according to claim 1.